With the recent upgrade of AppEngine Golang from go111 to go112 you might have to change your database DSNs if you’re using CloudSQL and want to connect using the /cloudsql/ socket.

DB DSN format for CloudSQL Postgres and Golang go112:

\

 "user=<<USER>> password=<<PWD> host=/cloudsql/<<CONNECTION NAME>>/ dbname=<<NAME>>"

The instance connection name can be found on Instance Detail page of Google Cloud Console. Make sure your AppEngine service account has at least the CloudSQL Client role.